Current responsive switching module

ABSTRACT

A reed relay mounted within a housing is responsive to a magnetic field induced in a flux-conducting clip mounted on an outer surface of the housing by current in a conductor passing through the clip. A flux diverting shield is placed over the relay in an adjusted position to provide the relay with a predetermined sensitivity to the magnetic field.

United States Patent Ries [4 1 June 13, 1972 [54] CURRENT RESPONSIVE SWITCHING 3,570,004 3 1971 De Jong ..335/151 MODULE 3,569,880 3/1971 Wahlgren ..335/204 Inventor: Robert G. Milwaukee Wis. 3,538,386 11/1970 Schweitzer, Jr ..335/204 [73] Assignee: Square D Company, Park Ridge, Ill. Primary Examiner-Remard A. Gilheany Assistant Examiner-R. N. Envall, Jr. [22] 1970 AttorneyHarold J. Rathbun and William 1-1. Schmeling [21] App]. No.: 95,163

[57] ABSTRACT 52] US. Cl ..335/204 A reed relay mounted ithi a h using is responsive to a mag- 1 Holh 51/28 netic field induced in a flux-conducting clip mounted on an [58] Field 0 Search 151, 154 outer surface of the housing current in a conductor p g through the clip. A flux diverting shield is placed over the [56] References cued relay in an adjusted position to provide the relay with a UNITED STATES PATENTS predetermined sensitivity to the magnetic field. 3,188,427 6/1965 Cooper et a1. ..335/204 5Clainu, 5 Drawing figures P'A'TENTEDJun 13 m2 FIG.

INVEN TOR. ROBERT G. RIES CURRENT RESPONSIVE SWITCHING MODULE The present invention relates to electrical circuit modules, and more particularly to a circuit module responsive to current in a motor circuit. In the example shown, the module is for controlling the series field of a direct current motor of a type useable for the traction drive of a battery powered truck.

To provide economical and efficient traction motor drive systems, the size of the motor must be minimized and the power output of the motor translated through a step down gear train to provide a relatively large torque at the driving wheels of the truck. Thus, industrial lift trucks are generally limited to operation at slow speeds so that they may be able to transport loads which are heavy in comparison with the horsepower of the traction motor. However, it is at times desirable to be able to propel a lift truck at speeds faster than normal load-carrying speeds, for example, when a truck is required to move over a level surface in a warehouse in an unloaded condition to a load pick-up point.

It is well known that the speed of a series motor increases when its field strength is reduced. This technique is commonly known as field weakening and may be accomplished with a circuit such as that disclosed in the concurrently filed application, Ser. No. 95,047, in the names of Robert G. Ries and Robert C. Montross and assigned to the assignee of the present invention. As shown in that applicatiomthe circuit must sense the presence of the low motor current which is present during high speed, light load operation and thereupon apply a shunt resistor to the field. It must also be able to remove the resistor when an increase in motor current indicates the existence of an increased motor load.

As described in the aforementioned application, the field weakening circuit comprises transistors and other small and delicate electrical components which must be commingled within the power system of the truck with much larger and more rugged electrical equipment such as the motor. When so used, the small components are susceptible to damage by being struck bythese larger objects when, for instance, the larger equipment is installed or repairs are being made to it. For this reason, it is desirable to provide a protective enclosure for the small components which, under normal use, prevents their being damaged by physical impact. Also, in manufacturing such circuits, it is often desirable that the constituent parts thereof be in convenient modular units to facilitate rapid replacement in order to minimize down time during repair.

. A field weakening circuit must operate in response to changes in motor current which, for battery-powered traction motors, is of relatively high value. When delicate electronic components are used to sense variations in large currents, it is a general practice in prior art devices to establisha voltage which is proportional to the current to be sensed and design the circuit to respond to variations in this voltage. However, with such an arrangement, performance on the truck may not be the same as performance obtained when the module is calibrated and preset during manufacture.

The module of the present invention, therefore, comprises a reed relay mounted within a housing of the module and responsive to changes in a magnetic field induced in a current sensitive clip which is mounted on an outer wall of the module housing. A conductor which carries the armature current of the motor passes through the clip for inducing the magnetic flux in the clip. A flux diverting shield is positioned around the reed relay contacts to control the sensitivity of the relay to the magnetic field. In this manner, the module can be accurately preset during manufacture and will operate in the same manner after installation on the truck.

These and other advantages of the switching module of the present invention will become apparent from the following description wherein reference is made to the drawings, in which:

FIG. 1 is a side view of a switching module constructed in accordance with the present invention with a side wall of a housing partially broken away;

FIG. 2 is an end view of the module of FIG. 1 shown with a conductor extending through a current sensing clip thereof;

FIG. 3 is a top view of the module of FIG. 1 with a cover member partially broken away;

FIG. 4 is an exploded perspective view of the current sensing clip and its mounting plate;

FIG. 5 is an exploded perspective view of a reed relay for use in the assembly of FIG. 1 and a shielding member made in accordance with the present invention. 4

Referring to the drawings, a field weakening module 11 has a housing comprising a base 12 molded of insulating material. Vertical ridges l3 FIG. 3) defining slots therebetween are preferably provided on the inner surfaces of opposite end.

walls of the base 12 across the full width thereof. The top of the base 12 is open and accommodates a cover member 14 also molded of insulating material and removably securable at the open top of the base 12 by screws 15 received in corresponding threaded apertures 12a in the base 12. The cover member 14 may be provided with a plurality of terminals 16 to facilitate external electrical connections of the module 1 l.

A circuit assembly 17 is mounted within the base 12 and comprises a plurality of circuit elements mounted on a circuit board 18 and operably inter-connected to form a motor control circuit or the like such as a field weakening circuit. A preferred field weakening circuit is disclosed in the aforementioned application, Ser. No. 95,047. The circuit assembly may be encapsulated in epoxy within the base 12 or may be removably held between opposite pairs of vertical ridges 13 within the base 12. Conductors 19 are connected respectively between inner portions of the terminals 16 and appropriate components of the circuit assembly 17. Sufficient slack should be provided in the conductors 19 to allow removal of the cover member 14, as for adjustment of a potentiometer 20, without disturbing the circuit assembly and, if the module 11 is encapsulated in epoxy, to avoid the necessity of disconnecting each conductor 19 from its corresponding terminal 16 whenever the module 11 is opened. Potentiometer adjustment may also be accommodated by openings 21 which may be provided at appropriate locations in the cover member 14.

The circuit assembly 17 includes one or more pairs of magnetically operated contacts, preferably the contacts of a reed relay 22, which is mounted on the circuit board 18 in close proximity to one wall portion 24 of the housing 12. A nonmagnetizable mounting plate 25 (best shown in FIG. 4) is attached to the wall portion 24 of the base 12, preferably by a screw 26 passed through an opening (not shown) in the wall portion 24 and secured in a threaded aperture 27 in the mounting plate 25.

A substantially U-shaped current sensitive clip 29 (best shown in FIG. 4) is formed of magnetizable material and has a bight portion 290, a pair of leg portions 29b, each preferably forming a right angle with the bight portion 29a, and a pair of outwardly turned mounting feet 29c disposed substantially parallel to each other and to the bight portion 29a of the clip. The clip 29 is mounted on the outer surface of the wall portion 24 by screws 30 which are inserted through openings 31 in each of the mounting feet 29c and through corresponding openings (not shown) in the wall portion 24 and which are received in threaded apertures 32 in the mounting plate 25.

The clip 29 and the wall portion 24 cooperate to define an opening 33 through which is passed a conductor 34 (FIG. 2). The conductor 34may be an armature lead for a direct current motor and carries the current to be sensed for determining the operation of the circuit assembly 17. The conductor 34 may be threaded between the clip 29 and the wall portion 24, or may be positioned by removing the screws 30 and correspondingly the clip 29, placing the conductor 34 against the base 12, and reattaching the clip 20 around the conductor 34.

It is well known that a magnetic field is formed around any conductor through which a current is flowing, and that the magnitude of the magnetic field is directly proportional to the magnitude of the current in the conductor. Thus a magnetic field will be induced in the clip 29 which varies in magnitude with the current flowing to the motor through the conductor 34.

Whenever a magnetic field is induced in the clip 29, there will be field in the air gap between the mounting feet 290. Thus the contacts of the reed relay 22 will become magnetized by the field in the air gap and will close due to magnetic attraction, in a manner well known in the art. However, reed relays are highly sensitive and the contacts will normally close even in the presence of a weak magnetic field. Because the conductor 34 is carrying a relatively large current, and because the position of the relay 22 is fixed and in close proximity to the clip 24, the relay contacts would tend to close at a current level too low to insure optimum operation of the circuit. To prevent this, a generally U-shaped magnetizable shielding member 35 is provided for the reed relay 22. The shielding member 35 diverts a portion of the induced magnetic flux from the contacts of the reed relay. The portion diverted is determined by the position of the shielding member with respect to the reed relay 22. As the shielding member 35 is moved in the direction of the arrow 36 in FIG. 5 and thereby covers more of the reed relay 22, a greater amount of magnetic flux is diverted from the contacts so that the contacts will remain open until a greater magnitude of magnetic flux is induced in the clip 29 and, consequently, until a higher level of current is passing through the conductor 34. In this manner the sensitivity of the reed relay 22 can be adjusted so that the contacts will open and close at the proper preselected motor current magnitudes.

The current values at which the contacts of the reed relay 22 will open and close can be accurately and reproduceably preset during manufacture and before final assembly of the module 11. Each clip 29 is manufactured in a manner to provide uniform magnetic characteristics; also, the distance between the reed relay 22 and the clip 29 in each module is constant. Therefore, each reed relay 22 can be correctly spaced from a clip 29 positioned around a conductor 34 which is carrying the value of current at which the contacts are to be actuated. The shielding member 35 may then be properly positioned to assure correct relay sensitivity. For example, the

shielding member 35 can be initially positioned for maximum shielding of the reed relay 22. In this position the relay contacts will be open. The shielding member 35 is now moved in the direction of the arrow 37 in FIG. 5 until the contacts of the reed relay 22 close. This is the correct location for the shielding member 35 and it is cemented or otherwise permanently affixed to the reed relay 22. In this manner the contacts can be tuned to respond to a particular magnitude of motor current and will respond in the same manner on the truck as when set during manufacture.

I claim:

1. An assembly comprising a plurality of operably inter-connected circuit elements including a pair of contacts responsive to selective application of a magnetic flux, a housing of nonmagnetizable material for containing the circuit elements with said contacts positioned a predetermined distance from an outer surface of a wall portion of said housing, clip means of magnetizable material mounted externally of said housing on said outer surface in flux producing relationship with a current conductor means, and shielding means for diverting a predetermined portion' of the magnetic flux from said contacts.

2. An assembly in accordance with claim 1 wherein said clip means is substantially U-shaped and is positioned around said current conductor means.

3. An assembly in accordance with claim 2 wherein said clip means is releasably mounted on said outer surface.

4. An assembly in accordance with claim 1 wherein said shielding means comprises a substantially U-shaped magnetizable member having its leg portions adjustably positioned on opposite sides of said contacts to cause said contacts to respond to a predetermined value of said magnetic flux.

5. An assembly in accordance with claim 4 wherein said contacts are contained in a non-magnetizable casing and the leg portions of said U-shaped magnetizable member are positioned on opposite sides of iaid caslng 

1. An assembly comprising a plurality of operably interconnected circuit elements including a pair of contacts responsive to selective application of a magnetic flux, a housing of non-magnetizable material for containing the circuit elements with said contacts positioned a predetermined distance from an outer surface of a wall portion of said housing, clip means of magnetizable material mounted externally of said housing on said outer surface in flux producing relationship with a current conductor means, and shielding means for diverting a predetermined portion of the magnetic flux from said contacts.
 2. An assembly in accordance with claim 1 wherein said clip means is substantially U-shaped and is positioned around said current conductor means.
 3. An assembly in accordance with claim 2 wherein said clip means is releasably mounted on said outer surface.
 4. An assembly in accordance with claim 1 wherein said shielding means comprises a substantially U-shaped magnetizable member having its leg portions adjustably positioned on opposite sides of said contacts to cause said contacts to respond to a predetermined value of said magnetic flux.
 5. An assembly in accordance with claim 4 wherein said contacts are contained in a non-magnetizable casing and the leg portions of said U-shaped magnetizable member are positioned on opposite sides of said casing. 